/*
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <algorithm>
#include <atomic>
#include <cassert>
#include <functional>
#include <iostream>
#include <memory>
#include <thread>
#include <utility>
#include <vector>

#include <folly/experimental/pushmi/executor/strand.h>
#include <folly/experimental/pushmi/o/just.h>
#include <folly/experimental/pushmi/o/transform.h>
#include <folly/experimental/pushmi/o/via.h>

#include <folly/experimental/pushmi/examples/pool.h>

// // See https://github.com/executors/futures-impl
// #include <futures.h>
// #include <futures_static_thread_pool.h>

using namespace folly::pushmi::aliases;

struct inline_executor {
 public:
  friend bool operator==(
      const inline_executor&,
      const inline_executor&) noexcept {
    return true;
  }
  friend bool operator!=(
      const inline_executor&,
      const inline_executor&) noexcept {
    return false;
  }
  template <class Function>
  void execute(Function f) const noexcept {
    f();
  }
  // constexpr bool query(std::experimental::execution::oneway_t) {
  //   return true;
  // }
  // constexpr bool query(std::experimental::execution::twoway_t) {
  //   return false;
  // }
  // constexpr bool query(std::experimental::execution::single_t) {
  //   return true;
  // }
};

// namespace p1054 {
// // A promise refers to a promise and is associated with a future,
// // either through type-erasure or through construction of an
// // underlying promise with an overload of make_promise_contract().
//
// // make_promise_contract() cannot be written to produce a lazy future.
// // The promise has to exist prior to .then() getting a continuation.
// // there must be a shared allocation to connect the promise and future.
// template <class T, class Executor>
// std::pair<
//     std::experimental::standard_promise<T>,
//     std::experimental::standard_future<T, std::decay_t<Executor>>>
// make_promise_contract(const Executor& e) {
//   std::experimental::standard_promise<T> promise;
//   auto ex = e;
//   return {promise, promise.get_future(std::move(ex))};
// }
//
// template <class Executor, class Function, class Future>
// std::experimental::standard_future<
//     std::result_of_t<
//         Function(std::decay_t<typename std::decay_t<Future>::value_type>&&)>,
//     std::decay_t<Executor>>
// then_execute(Executor&& e, Function&& f, Future&& pred) {
//   using V = std::decay_t<typename std::decay_t<Future>::value_type>;
//   using T = std::result_of_t<Function(V &&)>;
//   auto pc = make_promise_contract<T>(e);
//   auto p = std::get<0>(pc);
//   auto r = std::get<1>(pc);
//   ((Future &&) pred).then([e, p, f](V v) mutable {
//     e.execute([p, f, v]() mutable { p.set_value(f(v)); });
//     return 0;
//   });
//   return r;
// }
//
// } // namespace p1054

namespace p1055 {

template <class Executor, class Function, class Future>
auto then_execute(Executor&& e, Function&& f, Future&& pred) {
  return pred | op::via(mi::strands(e)) |
      op::transform([f](auto v) { return f(v); });
}

} // namespace p1055

int main() {
  mi::pool p{std::max(1u, std::thread::hardware_concurrency())};

  p1055::then_execute(p.executor(), [](int v) { return v * 2; }, op::just(21)) |
      op::get<int>;

  p.stop();
  p.wait();

  // std::experimental::futures_static_thread_pool sp{
  //     std::max(1u, std::thread::hardware_concurrency())};
  //
  // auto pc = p1054::make_promise_contract<int>(inline_executor{});
  // auto& pr = std::get<0>(pc);
  // auto& r = std::get<1>(pc);
  // auto f = p1054::then_execute(
  //     sp.executor(), [](int v) { return v * 2; }, std::move(r));
  // pr.set_value(42);
  // f.get();
  //
  // sp.stop();
  // sp.wait();

  std::cout << "OK" << std::endl;
}
